Relationships Between Spoken Word and Sign Processing in Children With Cochlear Implants

The effect of using signed communication on the spoken language development of deaf children with a cochlear implant (CI) is much debated. We report on two studies that investigated relationships between spoken word and sign processing in children with a CI who are exposed to signs in addition to spoken language. Study 1 assessed rapid word and sign learning in 13 children with a CI and found that performance in both language modalities correlated positively. Study 2 tested the effects of using sign-supported speech on spoken word processing in eight children with a CI, showing that simultaneously perceiving signs and spoken words does not negatively impact their spoken word recognition or learning. Together, these two studies suggest that sign exposure does not necessarily have a negative effect on speech processing in some children with a CI

Evidence that humans metabolize benzene via two pathways.

BACKGROUND: Recent evidence has shown that humans metabolize benzene more efficiently at environmental air concentrations than at concentrations > 1 ppm. This led us to speculate that an unidentified metabolic pathway was mainly responsible for benzene metabolism at ambient levels. OBJECTIVE: We statistically tested whether human metabolism of benzene is better fitted by a kinetic model having two pathways rather than one. METHODS: We fit Michaelis-Menten-like models to levels of urinary benzene metabolites and the corresponding air concentrations for 263 nonsmoking Chinese females. Estimated benzene concentrations ranged from less than 0.001 ppm to 299 ppm, with 10th and 90th percentile values of 0.002 ppm and 8.97 ppm, respectively. RESULTS: Using values of Akaike's information criterion obtained under the two models, we found strong statistical evidence favoring two metabolic pathways, with respective affinities (benzene air concentrations analogous to K(m) values) of 301 ppm for the low-affinity pathway (probably dominated by cytochrome P450 enzyme 2E1) and 0.594 ppm for the high-affinity pathway (unknown). The exposure-specific metabolite level predicted by our two-pathway model at nonsaturating concentrations was 184 muM/ppm of benzene, a value close to an independent estimate of 194 muM/ppm for a typical nonsmoking Chinese female. Our results indicate that a nonsmoking woman would metabolize about three times more benzene from the ambient environment under the two-pathway model (184 muM/ppm) than under the one-pathway model (68.6 muM/ppm). In fact, 73% of the ambient benzene dose would be metabolized via the unidentified high-affinity pathway. CONCLUSION: Because regulatory risk assessments have assumed nonsaturating metabolism of benzene in persons exposed to air concentrations well above 10 ppm, our findings suggest that the true leukemia risks could be substantially greater than currently thought at ambient levels of exposure-about 3-fold higher among nonsmoking females in the general population